1. Field of the Invention
The invention relates to a device for reducing the gas and water contamination of transformer oil fillings which is especially suitable for reducing air gas and air humidity contamination of power transformers oil fillings.
2. Description of the Related Art
The existing solutions for reducing the gas and water contamination of fluids can be distinguished according to the principles they utilize on the one hand, or the degree of protection which these solutions give to protected fluids on the other hand.
One of the examples well known from engineering practice is the protection of power transformer oil fillings against air gas and humidity infiltration from the surrounding atmosphere.
The most frequently used devices are limited to only reducing the air humidity infiltration into the transformer oil filling by using air dryers. The dryers, operating either on an absorption or a freezing principle, are usually inserted into the pipeline joining a dialation vessel (conservator) with surrounding atmosphere.
Another substantially more effective solution which is able not only to limit the air humidity infiltration, but also air gas infiltration into a protected oil filling, operates on the principle of an elastic element, which is usually a bag or a diaphragm built directly in a conservator, where by means of said element, the protected fluid is separated from the surrounding air.
A further solution consists in reducing the air and humidity infiltration into the main tank by a so called thermo-hydraulic closure which is embedded either directly in a conservator or in a pipeline connecting the top part of the main tank with the bottom part of a conservator. In this case, a so called thermal stratifying layer is utilized which arises in a thermo-hydraulic closure vessel and separates cold and potentially contaminated oil from the conservator from the hot oil in the main tank. Under suitable conditions this layer acts as a very thin and perfectly elastic diaphragm protecting the proper transformer oil filling against the infiltration of undesirable admixtures from the surroundings.
Another relatively new solution, which can strongly reduce the air gas and humidity infiltration into the oil filling of power transformers, utilizes a dissimilar hydraulic connection between the conservator and the main tank. The connection of the transformer bottom part with the conservator enables the exploitation of the thermal stratifying layer which spontaneously arises in the transformer bottom part of the main tank for a natural separation of the hot and clean oil which occurs in a top part of this machine from the air gas contaminated cold oil which occurs in the conservator.
All solutions given here and devices based thereupon have some disadvantages.
A fundamental disadvantage of all devices which merely suppress or reduce the air humidity infiltration into the transformer is they only affect the water contamination of the transformer and thereby the instant (short-term) reliability thereof. More particularly, these solutions do not limit the undesired penetration of gas, above all oxygen, into the transformer and are not able to suppress the oxidation aging both of the proper oil and of solid insulants which mainly affect the long-term reliability of this machine.
However, one fact to be considered as a main disadvantage of the so called transformer hermetization by means of a bag or diaphragm, built in a conservator, is that this solution is relatively expensive and routinely needs a tightness check of the elastic element in working conditions. When some leakage appears, this element cannot be simply repaired and usually the whole conservator must be replaced.
In a case where the thermo-hydraulic closure is used, some disadvantages of the elastic element do not occur because the thermal stratifying layer arises always spontaneously on a hot and cold oil boundary line and cannot be permanently damaged. But to stabilize this layer, a sufficient thermal difference must be maintained in a thermohydraulic closure vessel and—in order to cover the whole extent of transformer working temperatures—the thermo-hydraulic closure vessel must be sufficiently voluminous. All these facts complicate both the transformer design (usually so called transport profile thereof must be enlarged), and an eventual modification thereof to a hermetized version, and further additional devices are necessary which complicate the maintenance. For example, the thermal stratifying level must be stabilized by drawing out the oil from the closure.
A main disadvantage of the thermal stratifying level utilization in the bottom part of a main tank consists in a potential stability violation of this layer, partly by heat transfer from the machine magnetic circuit anchored at the vessel bottom and partly by a turbulent oil stream from the coolers. This is due to relatively high vessel entering velocity of the turbulent oil stream which may start the stratifying layer to first undulate or even be destroyed afterwards.